Afghan policemen remove a damaged vehicle Saturday after a powerful car bomb exploded in the outskirts of Kabul, Afghanistan. The suicide bomber targeted the site where a security agreement with the United States will be discussed.

KABUL, Afghanistan — A suicide car bomber tore through the Afghan capital Saturday, just hours after President Hamid Karzai announced U.S. and Afghan negotiators had agreed on a draft deal allowing U.S. troops to remain in the country beyond a 2014 deadline.

The blast, which killed six people near where thousands of tribal leaders will discuss the deal next week, was a bloody reminder of the insecurity plaguing the country after 12 years of war.

The suicide bomber attacked security forces protecting the Loya Jirga site, Interior Ministry spokesman Sediq Sediqqi said. He said the blast killed six people and wounded 22. Among the dead were two security personnel, he said.

Sediqqi said Afghan security forces had prior knowledge of the suicide bombing, but were unable to stop the attack. He did not elaborate.

No group immediately claimed the attack, though blame is likely to fall on the Taliban, who have adamantly opposed the presence of any foreign soldiers in Afghanistan.

Karzai called for the Loya Jirga, a national consultative assembly of tribal elders, which will begin meeting Thursday to discuss the proposal. Some 3,000 elders and influential figures will debate the Bilateral Security Agreement.

Without its approval, Afghanistan likely will refuse to sign the agreement. If the Loya Jirga does approve it, the agreement still requires final approval from parliament, Karzai said.

U.S. officials refused to comment on the draft, describing the effort as an ongoing diplomatic process. Karzai provided few details regarding how and when the draft was finalized, but said there still remain “differences” between Washington and Kabul on the deal.

Negotiations have been protracted and often acrimonious. In the end it took a surprise visit to Afghanistan in October by U.S. Secretary of State John Kerry to produce the outlines of a deal.

Earlier, two senior U.S. officials told The Associated Press that Afghanistan had sought specific security guarantees, particularly against cross-border incursions by insurgents from neighboring Pakistan.

Washington is cautious about any commitments that could lead to a conflict with Pakistan. The officials spoke on condition of anonymity because of the deal was still being negotiated.

Karzai described a laborious negotiation process that sometimes came down to fine details of phrasing.

“There was one word that we didn’t want in the agreement but (the U.S.) wanted it and in the end they agreed to not use that word,” he said, without identifying the offending word.

Karzai did not say what the draft said about U.S. service members’ immunity from prosecution in an Afghan court. They could still face prosecution in a U.S. court.

The sweeping document incorporates the Status of Forces Protection Agreement, which the U.S. signs with every country where its troops are stationed.